Is the blood clot from a recent surgery? I just lost my dear pet from what the vet claims as a blood clot probably in her brain- but from what I know, it was probably from a stroke. Others vets and internal vet doctors suggest that if you think your dog has a blood clot, do not massage the area as the clot may travel to different areas of their body.
I hope your dog is okay.
Yes,get her to a vet very quickly and please keep us posted.It's the best you can do for your dog and yourself.
When you say 'you think she has a blood clot in the lung' -has this been diagnosed by the vet? Just because she is 15 does not mean she should not get the best treatment, and there may be something the vet can do to relieve the symptoms of this, or even bust the clot.
A blood clot which blocks arteries in the lungs causes sudden breathing problems or rapid breathing, possible fever, and weakness.
But this could be caused by a number of underlying problems (all of which may well be treatable)
She could receive oxygen therapy, and/or clot-busting drugs.
I would say that the QUICKER you get her to the vet the better! Go do it now. A clot on the lung is serious, and she will be suffering right now, trying to breathe.
Please do post back and let us know how she's doing.